Folding knife



FIG. 1 is a perspective view of a folding knife showing my new design;

FIG. 2 is a frontal elevational view thereof;

FIG. 3 is a right side elevational view thereof, with a blade thereof extended;

FIG. 4 is a bottom plan view thereof; and,

FIG. 5 is a right side elevational view thereof, with the blade thereof retracted.

The broken line portions of the drawings are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a folding knife, as shown and described. 